薄膜结构的几何非线性分析

使用动力松弛法对薄膜结构进行静载分析，并提出一种方法处理皱折单元以确保荷载分析的可靠性。薄膜结构如果在某膜单元的单向应力方向发生皱折，其单元本身仍然能够继续承受荷载，因此提出索松弛单元和膜皱折单元处理薄膜的索松弛和膜皱折问题。就索网结构和薄膜结构分类给出算例进行静载分析，算例表明本文的方法可以有效处理索松弛单元和膜皱折单元，确保荷载分析的准确性。     

Controlled fabrication of hierarchically microstructured surfaces via surface wrinkling combined with template replication

In this paper,we present a simple method by combining surface wrinkling and template replication to create a series of hierarchical structures on polydimethylsiloxane(PDMS) elastomer.The primary stable lined patterns are formed by duplicating commercialized compact disk and digital versatile disk with PDMS.The secondary microscale patterns are from surface wrinkling,which is elicited by oxygen plasma(OP) treatment of the prestrained PDMS stamp followed with the prestrain release.By systematically varying the OP exposure duration,the prestrain,and the angle(θ) between the primary pattern orientation and the prestrain direction,we obtain highly ordered well-organized composite patterns from different patterning techniques and with different length scales and mechanical stabilities.     

Analysis of the Wrinkle of an Automobile Weather-Strip Seal in Bending

Weather-strip seals in automotive door systems play a major role in determining the door closing effort, isolating the passenger compartment from water and reducing the wind noise inside the vehicle. The phenomenon of a wrinkle often occurs in weather-strips when they are assembled on the door surfaces which have bent or twisted profiles. Wrinkles in automobile weather-strip seals will affect the closing effort and noise isolation characteristics of the automotive door system. The wrinkle of anethylene-propylene-diene (EPDM) automobile weather-strip seals when bent and the critical conditions for a wrinkle to develop were characterized in this study. The hyperelastic material behavior of the EPDM sponge and EPDM dense rubber in the seal were modeled using the Foam model and Mooney–Rivlin model, respectively. Then a finite element analysis (FEA) model of the automobile weather-strip seal in assembly was developed and analyzed using then on linear FEA software Marc. The deformation of the seal and the thickness decrease in the critical region where it was prone to wrinkle were obtained by this FEA method. Finally the critical criterion of wrinkling was determined by analysis of the reaction forces in the critical region. The proposed analysis method can shorten the product design cycle and decrease the design and trial-product cost considerably.     

Mechanical behavior and wrinkling patterns of phase-separated binary polymer blend film

The wrinkling of phase-separated binary polymer blend film was studied through combining the Monte Carlo (MC) simulation for morphologies with the lattice spring model (LSM) for mechanical properties. The information of morphology and structure obtained by use of MC simulation is input to the LSM composed of a three-dimensional network of springs, which allows us to determine the wrinkling and the mechanical properties of polymer blend film, such as strain, stress, and Young’s modulus. The simulated results show that the wrinkling of phase-separated binary polymer blend film is related not only to the structure of morphology, but also to the disparity in elastic moduli between polymers of blend. Our simulation results provide fundamental insight into the relationship between morphology, wrinkling, and mechanical properties for phase-separated polymer blend films and can yield guidelines for formulating blends with the desired mechanical behavior. The wrinkling results also reveal that the stretching of the phase-separated film can form the micro-template, which has a wide application prospect.     

Adhesion of nonplanar wrinkled surfaces

Topological patterns on polymer surfaces can significantly alter and control adhesion. In this study, the effect of surface wrinkles on a spherical surface on adhesion has been studied. Surface wrinkling induced by swelling of a crosslinked polydimethylsiloxane elastomer constrained by a stiff, thin surface layer (silicate) is used to produce topographic features of various length scales over a large curved area. By controlling the properties of the stiff layer and the applied strain conditions, surface wrinkles of varying amplitude and wavelength are obtained. The effect of wrinkle morphology on adhesion is quantified, and the results display a transition from enhancement of adhesion to decrease depending upon wrinkle dimensions. A simple phenomenological model is proposed that describes the change of adhesion behavior as a function of wrinkle morphology. Our results provide a critical understanding toward tuning the adhesion behavior of nonplanar surfaces consisting of periodic topographic structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

空间薄膜阵面结构褶皱的实验研究

阵面薄膜上的褶皱会显著影响航天器性能,褶皱控制也是薄膜航天器研发的难点。本文采用白光扫描技术,测试了一个正方形薄膜阵面结构在纯剪切作用下的褶皱特性。测试结果显示,随着剪切力的增大,结构膜面褶皱数增加,褶皱幅度增大,膜面平整度降低。随着膜面预应力的增大,膜面上的褶皱数略有增大,褶皱幅度有所减小,膜面平整度有所提高。测试结果还显示,膜面上粘结缝的存在、以及粘结缝与剪切力间的方位关系对膜面褶皱有复杂的影响。论文所得结论对薄膜阵面结构设计研发具有参考价值。     

基于表面起皱法的梯度图案的可控制备

报道了基于非刻蚀法的表面起皱机制来实现高分子薄膜表面的周期性梯度图案的简单可控制备.即对于处于机械拉伸状态的聚二甲基硅氧烷(PDMS)弹性基底,在其底部垫入"积木",而后对其进行紫外-臭氧(UVO)和氧等离子体(OP)的联合表面处理."积木"的加入引起了表面处理后表面硅氧层(SiOx)梯度厚度的形成,进而当释放拉伸应变后,诱导产生了梯度皱纹图案.结果表明:当UVO与OP联用处理时,不仅实现了较小拉伸应变下梯度皱纹形貌的制备,而且扩大了UVO单独使用时梯度皱纹周期的变化范围.通过OP与UVO的处理顺序和处理时间等因素的简单调节,进一步实现了不同梯度皱纹微结构的精细构筑.     

Controlling the surface buckling wrinkles by patterning the material system of hard-nano-film/soft-matter-substrate

Wrinkling and buckling of nano-films on the compliant substrate are always induced due to thermal deformation mismatch.This paper proposes effective means to control the surface wrinkling of thin film on the compliant substrate,which exploits the curvatures of the curve cracks designed on the stiff film.The procedures of the method are summarized as:1)curve patterns are fabricated on the surface of PDMS(Polydimethylsiloxane)substrate and then the aluminum film with the thickness of several hundred nano-meters is deposited on the substrate;2)the curve patterns are transferred onto the aluminum film and lead to cracking of the film along the curves.The cracking redistributes the stress in the compressed film on the substrate;3)on the concave side of the curve,the wrinkling of the film surface is suppressed to be identified as shielding effect and on the convex side the wrinkling of the film surface is induced to be identified as inductive effect.The shielding and inductive effects make the dis-ordered wrinkling and buckling controllable.This phenomenon provides a potential application in the fabrication of flexible electronic devices.     

Finite inflation of a hyperelastic toroidal membrane over a cylindrical rim

The present paper is devoted to the study of finite inflation of a hyperelastic toroidal membrane on a cylindrical rim under uniform internal pressure. Both compliant and rigid frictionless rims have been considered. The compliant cylindrical rim is modeled as a linear distributed stiffness. The initial cross-section of the torus is assumed to be circular, and the membrane material is assumed to be a homogeneous and isotropic Mooney–Rivlin solid. The problem is formulated as a two point boundary value problem and solved using a shooting method by employing the Nelder–Meads search technique. The optimization function is constructed on a two (three) dimensional search space for the compliant cylinder (rigid cylinder). The effect of the inflation pressure, material properties and elastic properties of the rim on the state of stretch and stress, and on the geometry of the inflated torus have been studied, and some interesting results have been obtained. The stability of the inflated configurations in terms of occurrence of the impending wrinkling state in the membrane has also been studied.     

Large eddy simulation of turbulent premixed flames using level-set G-equation

Level-set G-equation and stationary flamelet chemistry are used in large eddy simulation of a propane/air premixed turbulent flame stabilized by a bluff body. The aim was to study the interaction between the flame front and turbulent eddies, and in particular to examine the effect of sub-grid scale (SGS) eddies on the wrinkling of the flame surface. The results indicated that the two types of turbulence eddies—the resolved large scale eddies and the unresolved SGS eddies—have different effects on the flame. The fluctuation of the flame surface, which is responsible for the broadening of the time averaged mean flame brush by turbulence, depends on the large resolved turbulence eddies. Time averaged mean flow velocity, temperature, and major species concentrations mainly depend on the large scale resolved eddies. The unresolved SGS eddies contribute to the wrinkling at the SGS level and play an important role in the enhancement of the propagation speed of the resolved flame front. In addition, the spatially filtered intermediate species, such as radicals, and the spatially filtered reaction rates strongly depend on the small SGS eddies. The asymptotic behavior of flame wrinkling by the SGS eddies, with respect to the decrease in filter size and grid size, is investigated further using a simplified level-set equation in a model shear flow. It is shown that to minimize the influence of the SGS eddies, fine grid and filter size may have to be used.